Switching graphic pages

Hardware Hacking, Programming and Game Solutions/Cheats
pser1
Posts: 1655
Joined: Sun Mar 25, 2012 7:32 pm
Location: Barcelona (SPAIN)

Re: Switching graphic pages

Post by pser1 »

thanks for that info Ciaran,

I had seen and read a bit about the works of Linville, in fact a few days ago I was reverse engineering one of his .cas just to see if there is something new to learn.
And yes, coming to switching, he, cleverly, sets DP to $FF so that everything goes faster.

cheers
pere
pser1
Posts: 1655
Joined: Sun Mar 25, 2012 7:32 pm
Location: Barcelona (SPAIN)

Re: Switching graphic pages

Post by pser1 »

well, finally I could test the mixing of two SG24 images.
The firsl row is made of bytes with the 8 bits of same color in both images. These show still and normal.

Second and third rows are the result of mixing a byte that has left bits colored and right ones in black in one image
being the other image the contrary, left bits are black and right ones colored with another color different from the one in the other screen (C2 = 9-C1)
So we are focusing on blocks of 1 byte wide and 12 bytes high (what an ASCII character would occupy in this mode)

The result is painfull, worsed by the fact that the image is a small part of the screen and the photos I have taken are horrible, but the actual image on the Dragon screen
is not much beter than shown ... pity!

cheers
pere
2xSG24 before mixing.jpg
2xSG24 before mixing.jpg (44.02 KiB) Viewed 5898 times
2xSG24 after mixing.jpg
2xSG24 after mixing.jpg (51.93 KiB) Viewed 5898 times
sorchard
Posts: 530
Joined: Sat Jun 07, 2014 9:43 pm
Location: Norwich UK

Re: Switching graphic pages

Post by sorchard »

Yes, a pity the SG24 doesn't work so well, though it could be the monitor. Is it a CRT? The display can be distorted by bright areas so the two frames don't line up properly.

I've just discovered that it is possible to switch between Dragon 64 & Tano Dragon from the menu in xroar without changing the ROMs. This is really useful because the Tano Dragon is 60Hz and is a better match to my laptop display. It might work for you too and help with developing the mixed colour displays.
Stew
pser1
Posts: 1655
Joined: Sun Mar 25, 2012 7:32 pm
Location: Barcelona (SPAIN)

Re: Switching graphic pages

Post by pser1 »

it is a color TV
The signal comes from the Dragon Video output and goes to the Euroconnector.

I have tried Tano with XRoar and have got the same flickering despite I added "-tv-type ntsc" in the start parameters of XRoar

Thinking all over again, I think that we could mix two SG24 images that have black as background and then we combine colors
in the desired cells by putting the same or another color in each screen.
This way we could wait for 8x8 = 64 colors to be displayed ... never mixing them with black of course!
The only problem is the resolution of SG24, just 64x192 to show an image doesn't seem to be very useful


cheers
pere
sorchard
Posts: 530
Joined: Sat Jun 07, 2014 9:43 pm
Location: Norwich UK

Re: Switching graphic pages

Post by sorchard »

pser1 wrote:I have tried Tano with XRoar and have got the same flickering
Hmm. I must have got lucky. My laptop gives a nice smooth display with the Tano Dragon but I've just tried my PC at work and the display is nowhere near as nice. My laptop must have the right 60Hz by chance.
Stew
pser1
Posts: 1655
Joined: Sun Mar 25, 2012 7:32 pm
Location: Barcelona (SPAIN)

Re: Switching graphic pages

Post by pser1 »

well, paraphrasing EL&P i will say:
Oh, what a lucky man ... you are!

The truth is that the video output from my Dragon64 is not very good, and the results of mixing the two color palettes gives mixed colors that have an internal shift so the whole image seems to have movement ...
I have to say in defense of the result that this is the first approach I have made with a little Java apllication that simply substitutes each color in the BMP with a combination taken from a table and there is no 'intelligence' to try to get the best combination that will give a result as approximate as possible to the original, so the colors you see here, are not the same in the original :(

The photos don't suffer the bit move because they are just one flash. I attach them here

cheers
pere
PMODE3:SCREEN1,0
PMODE3:SCREEN1,0
ImageColorset1.jpg (47.2 KiB) Viewed 5872 times
PMODE3:SCREEN1,1
PMODE3:SCREEN1,1
ImageColorset2.jpg (45.66 KiB) Viewed 5872 times
Superimposed Image
Superimposed Image
MixedImage.jpg (46.48 KiB) Viewed 5872 times
sorchard
Posts: 530
Joined: Sat Jun 07, 2014 9:43 pm
Location: Norwich UK

Re: Switching graphic pages

Post by sorchard »

It's not a bad start. The mismatch doesn't look obvious in the photo.

The problem with older TVs is they are not really designed to display images from computers. The sides of the screen bend in response to the wild changes in beam current. More modern digital TVs should be better as they are controlled by more sophisticated electronics. On the other hand, there is a chance the flicker will be more noticeable on a fast LCD screen compared to a slow CRT.
Stew
pser1
Posts: 1655
Joined: Sun Mar 25, 2012 7:32 pm
Location: Barcelona (SPAIN)

Re: Switching graphic pages

Post by pser1 »

hello sorchard,

I am sure that the image will get better by far from the moment we will be able to use the appropiate color combination for each color that has the image to be converted.

My TV is not an old one (less than 4 years). I use the Euroconnector entry with a std cable that I found in internet.
I'm affraid that the weakest point in the video chain keeps being the vieo output signal that my D64 delivers.

Maybe using one of these converters that, according to the seller, enhances the video quality of old computers' output, it would show better.
Mixing colors on wide surfaces has no problem at all, but when it comes to combining different colors in 'neighbour' pixels is creates something like 'moire'
(for sure it is not that, but is an annoying move effect, despite the image is completly still)

cheers
pere
sorchard
Posts: 530
Joined: Sat Jun 07, 2014 9:43 pm
Location: Norwich UK

Re: Switching graphic pages

Post by sorchard »

Sorry pser1, I didn't mean to write off your TV. I misunderstood what kind of movement you were referring to.

Are you talking about the annoying sawtooth patterns that travel up and down vertical edges? Unfortunately this is a standard feature of Dragons. The problem here is the video display is timed by one crystal and the colours are timed by another crystal which makes the edges of colours move around due to varying phase difference between pixel frequency and colour burst frequency.

There is a trimmer capacitor on the main board near the power connecter that can be adjusted to reduce the appearance of the patterns but the setting has a tendency to drift with time. It's very sensitive and is best adjusted with a plastic trim tool. A metal screwdriver has enough capacitance to interfere with the adjustment.
Stew
pser1
Posts: 1655
Joined: Sun Mar 25, 2012 7:32 pm
Location: Barcelona (SPAIN)

Re: Switching graphic pages

Post by pser1 »

Hello sorchard,
don't worry, I can tell you that the TV set where my D64 is connected was very cheap, so not a state of the art (if it could help having better images)

Yes, the movement I didn't know how to explain is exactly what you have described ... is the vertical line between two small areas colored with different colors.
I remember back in the eighties, I had the Dragon opened (well right now it is too) so that we could adjust the TV signal when it drifted too much.
I thought that if one uses the video output, that trimmer was of not use ... thought it was just for PAL/NTSC TV signal

If the synchro problem between the two clocks is 'hardware' related ... maybe it could be changed?
I won't mind to add a daugther board if necessary!

cheers
pere
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